To serve their assigned purpose, orbital space systems frequently require relatively large space structures. Such structures may include booms for sensors, solar arrays, platforms and networks. Since the size of these structures precludes transport by the spacecraft, the requirements of such structures invariably include minimum packing volume and minimum weight. Another requirement of such structures, conditioned by the cost of payload space and weight in space flight is a high ratio of stiffness in the erected state to the weight of the structure. A further requirement may be that the structure be capable of being erected from a fixed location, e.g. from the cargo bay of a space shuttle. Additionally, the procedure for constructing the structure must not be overly complex and must preferably avoid the use of heavy, bulky or complicated parts or equipment.
In addition to optimum structural efficiency, a precise self-determined geometry is desired. The use of a precise geometry will simplify the initial construction process, as well as the process of making additions to a previously complete structure.
Existing structures for orbital systems are subject to a number of disadvantages. Self-deployable structures, which automatically unfold and position themselves in space, are generally not efficient. Such structures generally carry a weight penalty because of the self-deployment function. Space structure concepts which are capable of manual or automated construction have often failed to achieve the necessary stiffness-to-weight ratio, stowage efficiency, simplicity of assembly from a fixed location and the required precision.
By way of example, U.S. Pat. No. 4,259,821 to Bush discloses a truss structure formed from structural columns. Due to its complexity, the structure shown in the patent does not lend itself to an automated assembly method suited to the limitations of a space environment. Another example of a space-erectable structure is shown in U.S. Pat. No. 4,337,560 to Slysh. The structure shown in the latter patent lends itself to an automated assembly technique, but is subject to several of the disadvantages set forth above. In particular, the structure disclosed in Slysh is incapable of construction from one fixed location. To overcome the deficiency. Slysh provides an assembler trolley which crawls along the erected structure as the latter is built up during construction.